Field Study on the Law of Surface Subsidence in the High-Intensity Fully Mechanized Caving Mining Working Face with Shallow Thick Bedrock and Thin Epipedon in Hilly Areas

Shallow and thick coal seams occur extensively in hilly areas in Shanxi Province and Shaanxi Province, China. The surface damage and landslides caused by shallow fully mechanized caving mining have a very serious impact on the environment. To provide a theoretical and reference foundation for mine environmental protection in hilly settings, a research on surface movement of the high-intensity fully mechanized caving mining working face with shallow thick bedrock and thin epipedon (HIFMCMWFSTBTE) is urgently needed. In this study, using the P2 working face of a mine as the research object, three surface subsidence observation lines were arranged in this working face to analyze the dynamic change characteristics of surface subsidence. Besides, the law of surface movement, mining sufficiency, fracture development and distribution characteristics, subsidence speed, and surface movement duration of HIFMCMWFSTBTE in hilly areas were comparatively studied. The research results reveal that the upper part of the slope slides towards the downhill direction under the action of tensile stress or push stress. As a result, the range of the horizontal movement towards the downhill direction of the slope and the range of surface movement both increase, and the movement angle and boundary angle both decrease compared with the plain. HIFMCMWFSTBTE is prone to serious sudden discontinuous damage. Fractures on the gully region surface develop along the contour, forming a crisscross fracture network, and the fractures are not easy to close after being generated. HIFMCMWFSTBTE in hilly areas can achieve full mining more easily than those of other geological conditions. According to the field measurement, critical full mining can be achieved in P2 working face when the ratio of mining width to mining depth is 1.07. The surface movement duration of HIFMCMWFSTBTE in hilly areas is relatively short. Considerable subsidence will occur in the active stage, and the surface subsidence is sudden and violent. The measured surface stabilization time of the P2 working face is only 20% of the calculated value in the Specification for Coal Pillar Reservation and Coal Mining under Buildings, Water Bodies, Railways, and Main Shafts (hereinafter referred to as the Specification), indicating that the specification's empirical formula is inapplicable to the calculation of surface stabilization time of the P2 working face.

REDUCTION OF DUST REMOVAL OFF THE TAILING DUMPS SURFACES AS AN ELEMENT OF PREPERATION FOR RECLAMATION

Purpose. Analysis of issues of fixing the surfaces of sawdust tailings and their preparation for reclamation. Methods. The research is carried out on the basis of system and element-structural approaches with the use of generally accepted universal, specific scientific expert-analytical methods and modern methods of dust surface stabilization, expert-analytical methods and modern methods of dust surface stabilization. Results. The urgency of the problem of pollution of the air basin of Kryvyi Rih due to the removal of dust from the surfaces of tailings of mining and processing plants is considered. A brief description of these man-made neoplasms, such as unique man-made tracts; promising man-made deposits; objects of high potential ecological danger; powerful sources of pollution of environment; factors of degradation, fragmentation, transformation of flora and fauna; factors of formation of occupational risks, occupational and general morbidity of the population of the region. The factors influencing the processes of dust formation and determining the intensity of movement of dust fractions of tails are outlined. The purpose of the work is to analyze the issues of fixing the surfaces of sawdust tailings and their preparation for reclamation. A detailed description, characteristics, performance and disadvantages of the most common modern dust binders are given. The need for further search for long-acting agents that are able to effectively fix the surface of dust formation in all temperature ranges and in conditions of relatively low relative humidity and the surface layer of erosion-hazardous material is indicated. The prospects of using an aqueous solution of peat in order to fix the surfaces of tailings, rock dumps, prevention of dust in the air are determined. The physical, chemical and mechanical properties of the erosion-resistant coating based on the humate peat extract “Ideal” are analyzed. Recommendations on the method of using the tool, cost-effectiveness and advantages of the proposed technology as a component of preparation of man-made lands for reclamation are presented. It is established that the technology of treatment of tailings surfaces with peat-based solutions is able to: reduce the removal of dust into the air; promote the formation of a fertile layer of certain surfaces of tailings; potentiate the processes of natural overgrowth of man-made ecotopes; reduce the required amount of fertile soil during the reclamation of man-made objects after the end of service life, etc. The need for further comprehensive analysis of practical research results with detailing and concretization of basic generalizations is identified. Scientific novelty. The scientific novelty is to adapt the use of an aqueous solution of peat for use in the conditions of GOK Kryvbas in order to reduce air pollution by dust on the one hand and prepare for biological reclamation of disturbed areas. Practical significance. The proposed technology of treatment of tailings surfaces with peat-based solutions can be used in the Kryvyi Rih industrial region and is able to reduce dust removal into the air.